Monoalkyl cyclopentadiene compounds and processes for preparing same

ABSTRACT

The disclosure provides methodology for the synthesis of mono-alkylated cyclopentadiene structures, which can be obtained via fulvene intermediates. In one embodiment, the cyclopentadiene ring is substituted with a trialkylsilyl moiety, which enables the further reaction with certain metal halides to form metal adducts. For example, the monoalkyl cyclopentadienes substituted with a trimethylsilyl group can be reacted with TiCl 4  to provide R*CpTiCl 3  complexes, wherein R* is a group of the formula 
                         
wherein R 1  and R 2  are as defined herein.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 USC 119 of U.S. Provisional Patent Application No. 63/283,855, filed Nov. 29, 2021, the disclosure of which is hereby incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present disclosure generally relates to a process for preparing mono-alkylated cyclopentadiene compounds.

BACKGROUND

Cyclopentadienes are useful as intermediates to many other useful organic compounds. Certain alkyl-substituted cyclopentadienes are useful as synthetic lubricants. (See, for example, U.S. Pat. Nos. 5,144,095 and 5,012,022. Additionally, the cyclopentadiene structure can also be found in many of the so-called single site metallocene catalysts used to make polyolefins such as polyethylenes and polypropylenes. (See, for example, U.S. Pat. No. 7,579,415).

One inherent difficulty in the handling of cyclopentadiene is that it tends to dimerize via a Diels-Alder reaction. This dimerization proceeds at room temperature over a period of hours, but can be reversed by utilization of heating, which in some cases requires a cracking procedure. Additionally, in alkylation reactions utilizing a cyclopentadiene anion species, the formation of di- and tri-alkyl species can be encountered, which further complicates the synthetic regime by reducing yields and necessitating further separation and purification.

Thus, a need exists for improved methodology for the mono-alkylation of cyclopentadiene structures.

SUMMARY

In summary, the disclosure provides methodology for the selective synthesis of mono-alkylated cyclopentadiene structures, which can be obtained via fulvene intermediates. In one embodiment, the cyclopentadiene ring is substituted with a trialkylsilyl moiety, which enables the further reaction with certain metal halides to form metal complexes. For example, the monoalkyl cyclopentadienes substituted with a trimethylsilyl group can be reacted with TiCl₄ to provide R*CpTiCl₃ complexes, wherein R* is a group of the formula

wherein R¹ and R² are as defined below. In this highly-selective process, the resulting products are mono-alkylated, with no dialkylation products detectible via gas chromatography or NMR. In this regard, the process of the disclosure is particularly useful for preparing (mono)isopropyl-substituted cyclopentadiene.

DETAILED DESCRIPTION

As used in this specification and the appended claims, the singular forms “a”, “an”, and “the” include plural referents unless the content clearly dictates otherwise. As used in this specification and the appended claims, the term “or” is generally employed in its sense including “and/or” unless the content clearly dictates otherwise.

The term “about” generally refers to a range of numbers that is considered equivalent to the recited value (e.g., having the same function or result). In many instances, the term “about” may include numbers that are rounded to the nearest significant figure.

Numerical ranges expressed using endpoints include all numbers subsumed within that range (e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4 and 5).

In one aspect, the disclosure provides a process for preparing a compound of the Formula (I):

-   -   wherein R¹ and R² are independently chosen from hydrogen and         C₁-C₈ alkyl,     -   which comprises contacting a compound of the formula

with a protic reagent.

In one embodiment of this aspect, the protic reagent is water, optionally containing an acid such as HCl (hydrochloric acid). In another embodiment, the protic reagent is an alcohol or polyol, optionally containing an acid. In another embodiment, R¹ and R² are methyl. In another embodiment, the alcohol is chosen from a C₁-C₈ alcohol.

In another aspect, the disclosure provides a process for preparing a compound of the Formula (I):

-   -   wherein R¹ and R² are independently chosen from hydrogen and         C₁-C₈ alkyl;     -   which comprises contacting cyclopentadiene with a compound of         the formula

in the presence of a base,

-   -   thereby forming a compound of the formula

-   -   which is in turn treated with a dialkyl magnesium compound,         thereby forming a compound of the formula

-   -   which is in turn treated with a protic reagent to provide a         compound of Formula (I).

In general, the starting material fulvenes can be prepared by reacting cyclopentadiene with a ketone or aldehyde of the formula R¹—C(O)—R² in the presence of a base such as pyrrolidone or an alkali metal hydroxide. The magnesocene (2), shown in Scheme 1, is then formed by the reaction of the fulvene intermediate (1) with a dialkyl magnesium compound such as Mg(CH₂CH₂CH₂CH₃)₂, in a non-coordinating solvent such as hexanes. In this regard, suitable dialkyl magnesium compounds include compounds having alkyl groups capable of β-hydride elimination; examples include Mg(C₂-C₈ alkyl)₂, Mg(C₃-C₈ alkyl)₂, or Mg(C₄-C₈ alkyl)₂. Scheme 1 below outlines the general synthetic scheme for quenching the magnesocene (2) with either a protic reagent or a trialkylsilyl halide (such as trimethylsilyl chloride) to provide the desired compounds:

Scheme 1: General Synthetic Scheme for the Preparation of Monoalkyl-Cyclopentadienes

Accordingly, in a further aspect, the disclosure provides a process for preparing a compound of the Formula (II):

-   -   wherein R¹ and R² are independently chosen from hydrogen and         C₁-C₈ alkyl; and R³ is a group of the formula (C₁-C₄ alkyl)₃Si—,     -   which comprises contacting cyclopentadiene with a compound of         the formula

in a presence of a base,

-   -   thereby forming a compound of the formula

-   -   which is in turn treated with a dialkyl magnesium compound,         thereby forming a compound of the formula

-   -   which is in turn treated with a compound of the formula (C₁-C₄         alkyl)₃Si—X, wherein X is halo to provide a compound of the         Formula (II).

In certain embodiments, R¹ and R² are chosen from hydrogen, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, n-pentyl, isopentyl, sec-pentyl, n-hexyl, isohexyl, sec-hexyl, n-heptyl, isoheptyl, sec-heptyl, n-octyl, isooctyl, and sec-octyl. In one embodiment, each of R¹ and R² is methyl. In one embodiment, R³ is trimethylsilyl. In one embodiment, X is chosen from chloro, bromo, or iodo; in another embodiment, X is chloro.

The compounds of Formula (I) and Formula (II) are useful as intermediates in the synthesis of metallocene catalysts. Additionally, the compounds of Formula (II) are useful in the preparation of Group IV, Group V, and Group VI and metal-substituted compounds in the plus four oxidation state, via reaction with the corresponding metal halides. For example, the compound of the Formula (II), wherein R³ is trimethylsilyl, can be reacted with TiCl₄ to provide a R*CpTiCl₃ complex.

In the disclosure, the processes which begin with a substituted fulvene starting material thus enable the synthesis of exclusively monoalkyl-substituted compounds versus formation of multi-alkylated cyclopentadienyl species, which can occur in ordinary alkylation reaction approaches where the product can become deprotonated by the initial metal-Cp complex (i.e., anionic cyclopentadiene) prior to a second alkylation with, for example alkyl bromide. In the latter case, levels of multi-alkylation can range from 0.5-5 weight percent. Advantageously, the processes of the disclosure provide mono-alkylated species with no detectible levels of multi-alkylated species by gas chromatography (e.g., GC and GC-MS) or NMR. Thus, in a further embodiment, the processes of the disclosure provide products having less than 0.5 weight percent, less than 0.3, or less than 0.1 weight percent of multi-alkylated species, as determined by gas chromatography.

Additionally, given the substituted fulvene approach outlined herein, the disclosure further advantageously provides the products of Formula (I) and (II), devoid of dicyclopentadiene and mixed dicyclopentadiene species.

The compounds of Formula (I) and (II), i.e., monoalkyl-substituted cyclopentadienes, are also useful as intermediates in the synthesis of metallocene catalysts, useful in the synthesis of various polyolefins, or alternatively as intermediates for precursors useful in atomic layer deposition (ALD) and chemical vapor deposition (CVD).

EXAMPLES

Synthetic Procedure for the Preparation ^(i)PrCp and ^(i)PrCp-TMS

Step 1: Synthesis of 6,6-dimethylfulvene (1e)

Acetone (1000 g. 17.2 mol), methanol (3 L, 2360 g), and cyclopentadiene (“Cp”) (1138 g, 17.2 mmol) were added to flask. The resulting mixture was cooled to −10° C. Pyrrolidine (100 g, 1.4 mol) was added in portions while maintaining <0° C. temperatures. After pyrrolidine addition completion, the resulting mixture was stirred for 2 hours at −10° C. to 0° C. The reaction mixture was warmed to room temperature and stirred overnight. The resulting mixture cooled to 0-5° C., and an aqueous 4% acetic acid solution (3000 mL) was added. The resulting biphasic mixture was settled, and the aqueous layer discarded. The organic phase was washed with brine, and the residual solvents were removed with vacuum. 6,6-Dimethylfulvene (1740 g) was obtained in 95% yield and 96% purity by ¹H-NMR and GC. Further purification by distillation resulted in 90% yield and 99% purity by ¹H-NMR and GC.

Compounds 1 a-f were prepared with the same procedure with appropriate aldehydes/ketones.

Step 2: Synthesis of bis[1-isopropyl-2,4-cyclopentadiene-1-yl] Magnesium (2e)

6,6-Dimethylfulvene (21.2 g, 0.2 mol) and hexanes (50 mL) were added to a flask under nitrogen. 1M di-n-Butylmagnesium in heptanes (100 mL, 0.1 mol) was added dropwise while maintaining <50° C. temperatures. After the addition of di-n-butylmagnesium, the resulting solution stirred at room temperature overnight. Complete removal of volatiles under vacuum produced bis[1-isopropyl-2,4-cyclopentadiene-1-yl]magnesium (23.2 g) in 98.3% yield and 99% purity by ¹H-NMR.

Note: n-butyl-sec-butylmagnesium in hexanes can be used instead di-n-butylmagnesium heptanes.

Compounds 2a, 2c, 2e and 2f were prepared with the same procedure with appropriate fulvenes.

Step 3A: Synthesis of Isopropyl-Cp (3e)

Bis[1-isopropyl-2,4-cyclopentadiene-1-yl] magnesium (10 g) and hexanes (100 mL) were added into a flask under nitrogen. The resulting mixture was cooled to 0° C., and 0.1 M HCl (25 mL) was added dropwise while maintaining <5° C. temperatures. The resulting mixture was warmed to room temperature. The aqueous layer discarded, and the organic layer dried with anhydrous magnesium sulfate. The resulting mixture filtered. Hexanes removal under reduced pressure produced isopropyl cyclopentadiene (8.3 g, mixture of isomers) in 91% yield and 98% purity by ¹H-NMR and GC.

Note: Water, alcohols can be used instead of 0.1 M HCl solution.

Compounds 3a, 3c, 3e and 3f were prepared with the same procedure with appropriate bis(cyclopentadienyl)magnesium complexes.

Step 3B: Synthesis of Isopropyltrimethylsilyl-Cp (4e)

Bis[1-isopropyl-2,4-cyclopentadiene-1-yl] magnesium (10 g) and hexanes (100 mL) were added into a flask under nitrogen. The resulting mixture was cooled to 0° C., and trimethylsilyl chloride (9.3 g) added dropwise while maintaining <5° C. temperatures. The resulting mixture was warmed to room temperature and passed through a silica plug. Hexanes removal under reduced pressure produced isopropyltrimethylsilylcyclopentadiene (13.8 g, mixture of isomers) in 90% yield and 98% purity by ¹H-NMR.

Compounds 4c, 4e and 4f were prepared with the same procedure with appropriate bis(cyclopentadienyl)magnesium complexes.

TABLE 1 Summary of alkyl-Cps and alkyl-Cp-TMS materials RCp RCp yield % Purity Aldehyde/ Fulvene RCp₂Mg [NMR [¹H- Compound Ketone Yield % Yield % yield] NMR] EthylCp Acetalde- 40% (1a) 90% (2a) 75% 40% hyde (3 a) EtCp, 35% EtCp dimer PropylCp Propanal 52% (1b) — — — ButylCp Butanal 80% (1c) 98% (2c) 84% 97% (3 c) PentylCp Pentanal 62% (1d) — — — isopropylCp Acetone 90% (1e) 98% (2e) 90% (3e) 98% sec-butylCp sec- 83% (1f) 98% (2f) 82% (3f) 99% butanal EthylCpTMS Acetalde- 40% (1a) 90% (2a) — — hyde PropylCpTMS Propanal 52% (1b) — — — ButylCpTMS Butanal 80% (1c) 98% (2c) 84% (4c) 97% PentylCpTMS Pentanal 62% (1d) — — — isopropyl- Acetone 90% (1e) 98% (2e) 90% (4e) 98% CpTMS sec-butyl- sec- 83% (1f) 98% (2f) 82% (4f) 99% CpTMS butanal

ASPECTS

In a first aspect, the disclosure provides a process for preparing a compound of the Formula (I):

-   -   wherein R¹ and R² are independently chosen from hydrogen and         C₁-C₈ alkyl,     -   which comprises contacting a compound of the formula

with a protic reagent.

In a second aspect, the disclosure provides the process of the first aspect, wherein the protic reagent is water.

In a third aspect, the disclosure provides the process of the second aspect, wherein the water further comprises an acid.

In a fourth aspect, the disclosure provides the process of the first aspect, wherein the protic reagent is an alcohol or polyol.

In a fifth aspect, the disclosure provides the process of the fourth aspect, wherein the protic reagent further comprises an acid.

In a sixth aspect, the disclosure provides the process of any one of the first through the fifth aspects, wherein R¹ and R² are methyl.

In a seventh aspect, the disclosure provides the process of the fourth aspect, wherein the alcohol is chosen from a C₁-C₈ alcohol.

In an eighth aspect, the disclosure provides the process of any one of the first through the seventh aspects, wherein the compound of Formula (I) has less than about 0.5 weight percent, less than about 0.3 weight percent, or less than about 0.1 weight percent, of multi-alkylated species, as determined by gas chromatography.

In a ninth aspect, the disclosure provides the process of any one of the first through eighth aspects, wherein the compound of Formula (I) is devoid of dicyclopentadiene and mixed dicyclopentadiene species.

In a tenth aspect, the disclosure provides a process for preparing a compound of the Formula (I):

-   -   wherein R¹ and R² are independently chosen from hydrogen and         C₁-C₈ alkyl,     -   which comprises contacting cyclopentadiene with a compound of         the formula

in the presence of a base,

-   -   thereby forming a compound of the formula

-   -   which is in turn treated with a dialkyl magnesium compound,         thereby forming a compound of the formula

-   -   which is in turn treated with a protic reagent to provide a         compound of Formula (I).

In an eleventh aspect, the disclosure provides the process of the tenth aspect, wherein the protic reagent is water.

In a twelfth aspect, the disclosure provides the process of the eleventh aspect, wherein the water further comprises an acid.

In a thirteenth aspect, the disclosure provides the process of the tenth aspect, wherein the protic reagent is an alcohol or polyol.

In a fourteenth aspect, the disclosure provides the process of the thirteenth aspect, wherein the alcohol or polyol further comprises an acid.

In a fifteenth aspect, the disclosure provides the process of any one of the tenth through fourteenth aspects, wherein R¹ and R² are methyl.

In a sixteenth aspect, the disclosure provides the process of the thirteenth or fourteenth aspects, wherein the alcohol is chosen from a C₁-C₈ alcohol.

In a seventeenth aspect, the disclosure provides a process for preparing a compound of the Formula (II):

-   -   wherein R¹ and R² are independently chosen from hydrogen and         C₁-C₈ alkyl; and R³ is a group of the formula (C₁-C₄ alkyl)₃Si—,     -   which comprises contacting cyclopentadiene with a compound of         the formula

-   -   thereby forming a compound of the formula

-   -   which is in turn treated with a dialkyl magnesium compound,         thereby forming a compound of the formula

-   -   which is in turn treated with a compound of the formula (C₁-C₄         alkyl)₃Si—X, wherein X is halo to provide a compound of the         Formula (II).

In an eighteenth aspect, the disclosure provides the process of the seventeenth aspect, wherein each of R¹ and R² is methyl.

In a nineteenth aspect, the disclosure provides the process of the seventeenth or eighteenth aspects, wherein R³ is trimethylsilyl.

In a twentieth aspect, the disclosure provides the process of the seventeenth, eighteenth, or nineteenth aspects, wherein X is chloro.

In a twenty-first aspect, the disclosure provides the process of any one of the seventeenth through the twentieth aspects, wherein the compound of Formula (II) has less than about 0.5 weight percent, less than about 0.3 weight percent, or less than about 0.1 weight percent, of multi-alkylated species, as determined by gas chromatography.

In a twenty-second aspect, the disclosure provides the process of any one of the seventeenth through the twenty-first aspects, wherein the compound of Formula (II) is devoid of dicyclopentadiene and mixed dicyclopentadiene species.

In a twenty-third aspect, the disclosure provides the process of any one the seventeenth through the twenty-second aspects, further comprising the step of treating the compound of Formula (II) with a Group IV, Group V, or Group VI metal halide.

In a twenty-fourth aspect, the disclosure provides the process of the twenty-third aspect, wherein the metal halide is TiCl₄.

In a twenty-fifth aspect, the disclosure provides a compound of Formula (I):

-   -   wherein R¹ and R² are independently chosen from hydrogen and         C₁-C₈ alkyl, and wherein the compound of Formula (I) has less         than about 0.5 weight percent of multi-alkylated species, as         determined by gas chromatography.

In a twenty-sixth aspect, the disclosure provides the compound of the twenty-fifth aspect, wherein R¹ and R² are methyl.

In a twenty-seventh aspect, the disclosure provides the compound of twenty-fifth or twenty-sixth aspect, wherein the compound of Formula (I) is devoid of dicyclopentadiene and mixed dicyclopentadiene species.

In a twenty-eighth aspect, the disclosure provides a compound of Formula (I), as claimed in any of the twenty-fifth through twenty-seventh aspects, wherein the compound of Formula (I) has less than about 0.3 weight percent of multi-alkylated species, as determined by gas chromatography.

In a twenty-ninth aspect, the disclosure provides a compound of Formula (I), as claimed in any of the twenty-fifth through twenty-seventh aspects, wherein the compound of Formula (I) has less than about 0.1 weight percent of multi-alkylated species, as determined by gas chromatography.

In a thirtieth aspect, the disclosure provides a compound of Formula (II):

-   -   wherein R¹ and R² are independently chosen from hydrogen and         C₁-C₈ alkyl; and R³ is a group of the formula (C₁-C₄ alkyl)₃Si—,         wherein the compound of Formula (II) has less than about 0.5         weight percent of multi-alkylated species, as determined by gas         chromatography.

In a thirty-first aspect, the disclosure provides the compound of the thirtieth aspect, wherein R¹ and R² are methyl.

In a thirty-second aspect, the disclosure provides the compound of the thirtieth or thirty-first aspect, wherein the compound of Formula (II) is devoid of dicyclopentadiene and mixed dicyclopentadiene species.

In a thirty-third aspect, the disclosure provides a compound of Formula (II), as claimed in any of the thirtieth through thirty-second aspects, wherein the compound of Formula (II) has less than about 0.3 weight percent of multi-alkylated species, as determined by gas chromatography.

In a thirty-fourth aspect, the disclosure provides a compound of Formula (II), as claimed in any of the thirtieth through thirty-second aspects, wherein the compound of Formula (II) has less than about 0.1 weight percent of multi-alkylated species, as determined by gas chromatography.

Having thus described several illustrative embodiments of the present disclosure, those of skill in the art will readily appreciate that yet other embodiments may be made and used within the scope of the claims hereto attached. Numerous advantages of the disclosure covered by this document have been set forth in the foregoing description. It will be understood, however, that this disclosure is, in many respects, only illustrative. The disclosure's scope is, of course, defined in the language in which the appended claims are expressed. 

What is claimed is:
 1. A process for preparing a compound of the Formula (I):

wherein R¹ and R² are independently chosen from hydrogen and C₁-C₈ alkyl, the process comprising: contacting a compound of the formula

with a protic reagent.
 2. The process of claim 1, wherein the protic reagent is water.
 3. The process of claim 2, wherein the water further comprises an acid.
 4. The process of claim 1, wherein the protic reagent is an alcohol or polyol.
 5. The process of claim 4, wherein the protic reagent further comprises an acid.
 6. The process of claim 1, wherein R¹ and R² are methyl.
 7. The process of claim 4, wherein the alcohol is chosen from a C₁-C₈ alcohol.
 8. The process of claim 1, wherein the compound of Formula (I) has less than about 0.5 weight percent of multi-alkylated species, as determined by gas chromatography.
 9. The process of claim 1, wherein the compound of Formula (I) is devoid of dicyclopentadiene and mixed dicyclopentadiene species.
 10. A process for preparing a compound of the Formula (I):

wherein R¹ and R² are independently chosen from hydrogen and C₁-C₈ alkyl, the process comprising: contacting cyclopentadiene with a compound of the formula

in the presence of a base, thereby forming a compound of the formula

which is in turn treated with a dialkyl magnesium compound, thereby forming a compound of the formula

which is in turn treated with a protic reagent to provide a compound of Formula (I).
 11. The process of claim 10, wherein the protic reagent is water.
 12. The process of claim 11, wherein the water further comprises an acid.
 13. The process of claim 10, wherein the protic reagent is an alcohol or polyol.
 14. The process of claim 13, wherein the alcohol or polyol further comprises an acid.
 15. The process of claim 1, wherein R¹ and R² are methyl.
 16. The process of claim 13, wherein the alcohol is chosen from a C₁-C₈ alcohol. 